I have a yz125 that had a clutch fiber disentegrate. Little chunks all over in it. I pulled off the cover and removed tiny pieces from around the clutch area, until I could find no more. Problem was that a piece found its way into the transmission. It wedged itself between the case and gears. I could not get the bike to shift, almost impossible to get into neutral, and it would get stuck in third. I bought shift forks and drum, expecting the worst, but it was just the clutch fiber chunks holding the gears from moving. I couldn't be sure what was going on until we split the cases and examined it, but that was the problem for me.